Abstract: River hydrological regime is regarded to be the key driver of river ecosystem. In order to study the alternation of the hydrological regime of the Jialing River basin caused by the construction of water conservancy projects, the change characteristics of flow regime were evaluated by using the Mann-Kendall statistical test, the cumulative departure and moving T detected method based on daily flow series at the representative hydrological station of the Jialing River-Beibei Station from 1956 to 2017, while the hydrologic regime alteration degree and fish ecological effect of Jialing River on the variation of 32 hydrological indexes were also analyzed by the range of variability approach and hydrologic regime alteration degree method. The results show that annual average flow of the Jialing River has shown a decreasing trend during 1956 to 2017. The abrupt junction of annual average flow is 1993 year. Through the analysis of the eco-hydrological indicators before and after the change of hydrological regime, it is concluded that the alternation degree of Beibei gauge station was 50%. The overall degree of hydrological alternation belongs to moderate alternation, and the change degree of the hydrological index of the number of reversals reaches 100%. Compared with the changes in fish composition, the number of some drifting fishes and large economic fishes adapted to the torrent habitat decreased significantly, and it was concluded that the operation of the trapezoidal reservoir in Jialing River had a great impact on fish diversity. This study can provide reference for ecological restoration and sustainable development of Jialing River Basin.